This pilot research proposal aims at the molecular identification and chromosomal localization of a major gene responsible for human cleft lip with or without cleft palate (CL(P)). The evidence for a major gene in clefting comes from recent publications by several authors using complex segregation analysis techniques. In these reports, two caucasian populations support the presence of a dominant gene with low penetrance. In this pilot study, a small number of caucasian families (2-3) showing multiple cases of non-syndromic CL(P) in multiple generations will be studied. The following molecular approaches to gene identification will be used: (1) restriction endonuclease enzymes to generate RFLPs which are then used as genetic markers. (2) GT sequences of chromosomal DNA generated by polymerase chain reaction (PCR) from specific primers. These dinucleotide sequences which are highly polymorphic are excellent genetic markers for gene linkage studies. The linkage studies will use the programs LIPED and LINKAGE to establish correlations between electrophoretic phenotypes obtained in (1) and (2) above and the cleft status. In these preliminary studies only selected chromosome areas will be probed for a major clefting gene. These areas are identified as the most likely to yield a positive result based upon (1) localization of clefting genes in the mouse and (2) reports in humans suggesting linkage between known markers and a cleft phenotype (HLA, F13A, etc.) and chromosome abnormalities (deletion syndromes) which may pinpoint the gene. Since gene penetrance has been identified as a problem in the complex segregation analysis studies, we will minimize the problem by using cephalometric identification of facial features in persons who are not cleft themselves but are at risk for transmitting the clefting trait (gene carriers). Penetrance of this major gene is estimated by segregation analysis to be 30%. With the use of the cephalometric technique we can improve this value to nearly 70%. This represents a considerable improvement in identification of gene carriers and hence an increased precision in identifying the cleft genotype.